Applications including varying LED die architectures are known. Vias are created in areas of LED arrangements where electrical contact is desired. It is understood by those of ordinary skill in the art that mobile atoms such as silver (Ag) and aluminum (Al) can migrate or otherwise relocate into vias during deposition or in subsequent processing steps.
This is particularly a problem in certain LED dies because Ag is known to contaminate the underlying epitaxy. The typical method for preventing contamination is to provide a barrier layer (or dielectric layer 114 as shown in FIG. 1) and a large offset between the via in the underlying barrier material and the via in the Ag layer. The Ag layer is subsequently sealed by capping with a guard sheet material, such as nickel (Ni) or tungsten (W), which results in a reduction in the total surface area of the Ag layer and reduces the reflective area on each LED die.
Producing LED dies typically involves multiple rounds of masking and photolithography, which requires a large via size in the second deposition layer to provide a margin for issues resulting from via misalignment. This mismatch in the size of vias between the first and second deposition layers defines the size of a critical dimension (CD) and if etching is used to form the via, this results in a large undercut, causing an enlarged CD.
Etching for semiconductor materials is well known, and is described in U.S. Pat. No. 9,583,353, which is incorporated by reference as if fully set forth herein. Applications including wafer bonding for LED architecture are also well known. One other known type of LED die is disclosed in U.S. Pat. No. 8,154,042, which is incorporated by reference as if fully set forth herein. These known types of devices have produced significant increases in light output. However, there are still contamination issues.
The reflective layer in LED dies contaminates the associated metal contact in a variety of ways. Contamination can occur due to direct deposition on top of contact metal, the reflective film anneal process, incursion of etch products in contact with the via during the etch process of the reflective layer, and/or voiding in a subsequent bonding layer due to removal of material from the first barrier layer during formation of the reflective layer. If trace elements of reflective film come into electrical contact with the underlying epitaxy, then a consistent high forward voltage can result.
It would be desirable to provide a reliable method of preventing contamination of the metal contacts in an LED die.